Regarding the freezing damage of high-grade highway subgrade in seasonally frozen area,the thesis explores the effect on the dynamic behavior of subgrade soil under freeze–thaw cycles and draws the change law of parameters(including dynamic strength,dynamic cohesion,and internal friction angle;and dynamic elastic modulus)of high-grade highway-subgrade soil with the number of freeze–thaw cycles.It aims to provide the reference for operation and maintenance of a high-grade highway.Conclusions:(1)Dynamic strength tends to decline evidently after freeze–thaw cycles,with 60%~70%decline after three cycles,and remains stable after five to seven cycles.(2)With the number of freeze–thaw cycles increasing,the internal friction angle fluctuates within a certain range without an obvious change law,only presenting the tendency of dropping off.The dynamic cohesion declines obviously,about 20%~40%after seven freeze–thaw cycles,and then tends to be stable.(3)With the number of freeze-thaw cycles increasing,the dynamic elastic modulus and maximum dynamic elastic modulus are inclined to decrease distinctly.After five freeze–thaw cycles,the former declines 30%~40%and then remains stable.Meanwhile,the latter falls 20%~40%. Regarding the freezing damage of high-grade highway subgrade in seasonally frozen area, the debate on the dynamic behavior of subgrade soil under freeze-thaw cycles and draws the change law of parameters (including dynamic strength, dynamic cohesion, and internal friction angle and dynamic elastic modulus of high-grade highway-subgrade soil with the number of freeze-thaw cycles. It aims to provide the reference for operation and maintenance of a high-grade highway. Conclusions: (1) Dynamic strength tends to decline evidently after freeze-thaw cycles, with 60% ~ 70% decline after three cycles, and remains stable after five to seven cycles. (2) With the number of freeze-thaw cycles increasing, the internal friction angle fluctuates within a certain range without an obvious change law, only presenting the tendency of dropping off. The dynamic cohesion declines obviously, about 20% ~ 40% after seven freeze-thaw cycles, and then tends to be stable. (3) With the number of freeze-thaw cy cles increasing, the dynamic elastic modulus and maximum dynamic elastic modulus are inclined to decrease distinctly. After five freeze-thaw cycles, the former declines between 30% and 40% and then remains stable.